Thanks for all your replies everyone. I reckon the washers fallen out and I've not seen it as the access to the feed pipe is a right pain.
Fantastic.
Thank you
Evening
Had an overflowing cold water tank which feeds my immersion heater so I decided to replace the high pressure ballcock valve which is fed from the mains.
Got everything fitted back together and now there is a slight leak where the mains pipe fits into the valve. Refitted it about...